A paper-based self-pumping microfluidic fuel cell stack with a novel vertical structure

Microfluidic fuel cell (MFC) stacking is a prerequisite to enhance its power output for practical applications. However, most MFC stacks reported in the present literature require external pumps to maintain the co-laminar flow and complex fluidic management networks for homogeneous flow and reactant distributions. To address these issues, a novel paper-based self-pumping MFC stack with potassium formate as the fuel and hydrogen peroxide as the oxidant is proposed in this study. The capillary action is employed to achieve passive liquid flow. A vertical stack structure with the unit cells piled one above another compactly is adopted to reduce the volumetric costs. The experimental results show that the maximum power outputs of the two-cell and three-cell stack prototypes are 4.01 and 7.26 mW cm⁻², outperforming the MFC unit by 5.81 and 10.52 times, respectively. The superior performance is attributed to its distinct vertical stacking structure, which brings the enhanced capillary flows in the paper wicks and reduced ohmic losses in comparison with the unit cell. Further, effects of the filter paper and reactant concentrations on the stack performance were examined, and mass transfer of the fuel and/or oxidant to the electrode/electrolyte interface was identified as the main limiting factor. A loose microstructure of the paper wick was found beneficial in enhancing the mass transfer. The potential applications of the MFC stack in a variety of portable electronics are broad.